U.S. patent application number 11/629858 was filed with the patent office on 2009-02-05 for laminated film for reflection plate.
This patent application is currently assigned to Teijin Dupont Films Japan Limited. Invention is credited to Hiroshi Kusume, Atsushi Oyamatsu.
Application Number | 20090035544 11/629858 |
Document ID | / |
Family ID | 35509527 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090035544 |
Kind Code |
A1 |
Kusume; Hiroshi ; et
al. |
February 5, 2009 |
Laminated film for reflection plate
Abstract
A laminated film for a reflecting plate is provided that
comprises a layer A and a layer B, the layer A comprising a
polyester that comprises substantially no antimony element and
preferably comprises 1 to 25 wt % of inert particles having an
average particle diameter of 0.3 to 3.0 .mu.m and the layer B being
in contact with the layer A and comprising a polyester which
preferably comprises 31 to 80 wt % of inert particles having an
average particle diameter of 0.3 to 3.0 .mu.m. This laminated film
has a practically satisfactory capability of reflecting visible
light, can be produced stably even if inert particles are added in
high concentration, hardly has streak-like defects, and can be
suitably used as a substrate for a reflecting plate for a liquid
crystal display or an internally illuminating electrical
billboard.
Inventors: |
Kusume; Hiroshi; (Gifu,
JP) ; Oyamatsu; Atsushi; (Gifu, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Teijin Dupont Films Japan
Limited
Tokyo
JP
|
Family ID: |
35509527 |
Appl. No.: |
11/629858 |
Filed: |
June 16, 2005 |
PCT Filed: |
June 16, 2005 |
PCT NO: |
PCT/JP05/11489 |
371 Date: |
December 18, 2006 |
Current U.S.
Class: |
428/213 ;
428/323; 428/335; 428/337; 528/308 |
Current CPC
Class: |
Y10T 428/10 20150115;
Y10T 428/2495 20150115; B32B 27/18 20130101; Y10T 428/24975
20150115; Y10T 428/25 20150115; Y10T 428/24967 20150115; Y10T
428/31786 20150401; Y10T 428/264 20150115; B32B 2307/416 20130101;
Y10T 428/266 20150115; B32B 2457/202 20130101; B32B 27/08 20130101;
B32B 27/36 20130101; C09K 2323/00 20200801; B32B 2309/105 20130101;
Y10T 428/24942 20150115 |
Class at
Publication: |
428/213 ;
428/323; 428/335; 428/337; 528/308 |
International
Class: |
B32B 5/16 20060101
B32B005/16; C08G 63/12 20060101 C08G063/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2004 |
JP |
2004-179388 |
Claims
1. A laminated film for a reflecting plate, which comprises at
least two layers one of which is a surface layer comprising an
aromatic polyester which comprises substantially no antimony
element.
2. The laminated film of claim 1, wherein the surface layer which
is one of the at least two layers comprises 1 to 25 wt % of inert
particles having an average particle diameter of 0.3 to 3.0
.mu.m.
3. The laminated film of claim 1, wherein the other layer other
than the surface layer comprises an aromatic polyester containing
31 to 80 wt % of inert particles having an average particle
diameter of 0.3 to 3.0 .mu.m.
4. The laminated film of claim 3, wherein the aromatic polyester is
a copolyester having a melting point of 220 to 250.degree. C.
5. The laminated film of claim 1, wherein the thickness of the
surface layer is 5 to 50 .mu.m.
6. The laminated film of claim 3, wherein the thickness of the
other layer other than the surface layer is 30 to 230 .mu.m.
7. The laminated film of claim 3, wherein the ratio of the
thickness of the surface layer/the thickness of the other layer
other than the surface layer is 1/20 to 1/2.
8. A method of using a laminated film, comprising preparing a
reflecting plate from the laminated film of claim 1.
9. The method of claim 8, wherein the reflecting plate is a
reflecting plate for a liquid crystal display.
10. A reflecting plate comprising the laminated film of claim
1.
11. The laminated film of claim 2, wherein the thickness of the
surface layer is 5 to 50 .mu.m.
Description
TECHNICAL FIELD
[0001] This invention relates to a laminated film for a reflecting
plate. More specifically, it relates to a laminated film that has
high reflectivity and hardly has film defects.
BACKGROUND ART
[0002] Liquid crystal displays have adopted a backlighting system
which lights the display from the back side thereof. However, in
recent years, such a sidelighting system as described in Japanese
Patent Laid-Open Publication No. 63-62104 has been widely used due
to an advantage that the display can be made thin and can be lit
uniformly. This sidelighting system is a system that applies light
to the display from cold-cathode tubes or the like from the edge of
an acrylic plate or the like having certain thickness, and due to
dot printing, illuminating light is dispersed uniformly, resulting
in a screen having uniform brightness. This system has an advantage
of making the liquid crystal display thinner than the backlighting
system because it places light sources not on the back side but on
the edge of the screen. However, a reflecting plate needs to be
placed on the back side of the screen to prevent illuminating light
from escaping to the back side of the screen. Accordingly, the
reflecting plate is required to have high light reflectivity and
high light diffusibility.
[0003] As a method for obtaining a polyester film suited for a
liquid crystal display reflecting plate which meets this purpose, a
method of incorporating an incompatible resin is described in
Japanese Patent Publication No. 8-16175. Although this method is a
method which can produce the above film at relatively low cost, it
is unsatisfactory in terms of an improvement in reflectivity since
it merely adds the incompatible resin, and the brightness of the
screen of a produced liquid crystal display is also unsatisfactory.
Further, when inert particles such as titanium oxide are added in
high concentration, an improvement in reflectivity can be expected.
However, when the inert particles are added in an amount of, for
example, 50 wt %, the concentration of the inert particles is so
high that ruptures often occur and film formation is very
difficult. Accordingly, a white polyester film which achieves a
good balance between an improvement in reflectivity and ease of
film formation has been needed.
[0004] Further, for conventional white polyester films, antimony
trioxide has been widely used as a catalyst as described in
Japanese Patent Laid-Open Publication Nos. 63-137927 and 63-235338.
Antimony oxide is liable to be deposited on a die when a molten
polyester resin is extruded from the die, and the deposited
antimony oxide is liable to produce streak-like defects on the
molten resin. In particular, in the case of white polyester films,
the streak-like defects are easily observed as black streak-like
defects. Therefore, measures therefor have been desired.
DISCLOSURE OF THE INVENTION
[0005] An object of the present invention is to provide a laminated
film for a reflecting plate which has a practically satisfactory
capability of reflecting visible light, can be produced stably even
if inert particles are added in high concentration and hardly has
streak-like defects thereon.
[0006] Another object of the present invention is to provide a
white laminated film that can be suitably used as a substrate for a
reflecting plate for a liquid crystal display or an internally
illuminating electrical billboard.
[0007] Other objects and advantages of the present invention will
become apparent from the following description.
[0008] According to the present invention, firstly, the above
objects and advantages of the present invention are achieved by a
laminated film for a reflecting plate, which comprises at least two
layers one of which is a surface layer comprising an aromatic
polyester which substantially contains no antimony element.
[0009] According to the present invention, secondly, the above
objects and advantages of the present invention are achieved by a
reflecting plate comprising the above laminated film.
PREFERRED EMBODIMENTS OF THE INVENTION
[0010] The laminated film of the present invention comprises at
least two layers. One of the layers is a surface layer, and the
surface layer comprises an aromatic polyester which substantially
contains no antimony element. Hereinafter, the surface layer will
be referred to as "layer A", and the other layer of the two layers
will be referred to as "layer B" for the purpose of simplifying the
following description.
[0011] The aromatic polyester used in the layers A and B comprises
an aromatic dicarboxylic acid component and a diol component as
main components. Illustrative examples of the aromatic dicarboxylic
acid include terephthalic acid, isophthalic acid,
2,6-naphthalenedicarboxylic acid, and 4,4'-diphenyldicarboxylic
acid. Illustrative examples of the diol include ethylene glycol,
1,4-butanediol, 1,4-cyclohexane dimethanol, and 1,6-hexanediol.
[0012] The aromatic polyester may be a homopolymer or a copolymer.
When it is a copolymer, an aliphatic dicarboxylic acid as a
dicarboxylic acid component can be used as a copolymerizable
component. Illustrative examples of the aliphatic dicarboxylic acid
include adipic acid and sebacic acid. The aromatic polyester is
preferably a homopolymer, that is, polyethylene terephthalate, or
copolymer comprising ethylene terephthalate as a main recurring
unit. In the case of the copolymer, the proportion of the
copolymerizable component is preferably 1 to 30 mol %, more
preferably 3 to 25 mol %, much more preferably 5 to 20 mol %,
particularly preferably 7 to 15 mol % of all dicarboxylic acid
components. When the proportion is lower than 1 mol %, a layer
containing inert particles, e.g. a layer containing at least 31 wt
% of inert particles, cannot be formed disadvantageously, while
when the proportion is higher than 30 mol %, a film having
unsatisfactory thermal and dimensional stability is obtained or
even film formation may not be achieved disadvantageously.
[0013] Of the layers A and B, the polyester used in at least the
layer A must contain substantially no antimony element.
Accordingly, polymerization of the polyester is conducted without
using an antimony compound as a catalyst. As a catalyst used in
polymerization of the polyester, any of a manganese (Mn) compound,
a titanium (Ti) compound and a germanium (Ge) compound is
preferably used, for example. Specific examples of the titanium
compound include titanium tetrabutoxide and titanium acetate.
Specific examples of the germanium compound include 1) amorphous
germanium oxide, 2) fine crystalline germanium oxide, 3) a solution
prepared by dissolving germanium oxide in glycol in the presence of
alkali metal or alkaline earth metal or a compound thereof, and 4)
a solution prepared by dissolving germanium oxide in water. A
method using these germanium compounds as a catalyst is known as a
method of polymerizing a polyester and is suitable as a method of
producing the polyester that is used in the present invention. The
polyester used in the layer B can also be produced by the same
method.
[0014] The phrase "containing substantially no antimony element"
indicates that the content of antimony element is 20 ppm or lower,
preferably 15 ppm or lower, more preferably 10 ppm or lower.
[0015] The melting point of the polyester of the layer B is
preferably 220 to 250.degree. C. By use of a polyester whose
melting point falls within this range, a film which can be produced
stably even if inert particles are added in high concentration can
be obtained.
[0016] The polyesters used in the layers A and B may contain
various known additives such as an antioxidant, antistatic agent,
fluorescent brightener and ultraviolet absorber.
Inert Particles
[0017] The polyester of the layer A in the present invention
preferably contains 1 to 25 wt % of inert particles having an
average particle diameter of 0.3 to 3.0 .mu.m. The polyester of the
layer B preferably contains 31 to 80 wt % of inert particles having
an average particle diameter of 0.3 to 3.0 .mu.m. The average
particle diameter of the inert particles contained in the layers A
and B is 0.3 to 3.0 .mu.m, preferably 0.5 to 2.5 .mu.m, more
preferably 0.7 to 2.0 .mu.m. When the average particle diameter is
smaller than 0.3 .mu.m, dispersibility deteriorates considerably
and agglomeration of the particles occurs. Consequently, troubles
in a production process are liable to occur, possibly resulting in
a film having coarse projections and poor gloss. Meanwhile, when
the average particle diameter is larger than 3.0 .mu.m, the
surfaces of the film becomes rough, resulting in degradation in
gloss, and it becomes difficult to control glossiness to a proper
range. Further, the half width of the particle size distribution of
the inert particles is preferably 0.3 to 3.0 .mu.m, more preferably
0.3 to 2.5 .mu.m.
[0018] Further, the content of the above inert particles in the
layer A is more preferably 2 to 23 wt %, particularly preferably 3
to 20 wt %. Likewise, the content of the above inert particles in
the layer B is more preferably 33 to 70 wt %, particularly
preferably 35 to 55 wt %.
[0019] Further, the proportion of the inert particles to the total
weight of the layers A and B is preferably 10 to 80 wt %, more
preferably 15 to 70 wt %, much more preferably 20 to 60 wt %,
particularly preferably 25 to 55 wt %. When the content of the
inert particles in the film is lower than 10 wt %, required
reflectivity and whiteness cannot be obtained, while when the
content of the inert particles is higher than 80 wt %, ruptures are
liable to occur during film formation disadvantageously.
[0020] As the inert particles, inorganic particles or organic
particles can be used. Illustrative examples of the organic
particles include a cross-linked polystyrene resin and a
cross-linked acrylic resin. Illustrative examples of the inorganic
particles include titanium oxide, barium sulfate, calcium carbonate
and silicon dioxide. These inorganic particles are so-called white
pigments and are preferably used to improve a reflective
performance. Of these, barium sulfate is particularly preferred
from the viewpoint of obtaining excellent reflectivity. Barium
sulfate may be plate-like particles or spherical particles.
[0021] When titanium oxide is used, rutile-type titanium oxide is
preferably used because yellowing of the polyester film after the
film is irradiated with light for a long time is less severe with
the rutile-type titanium oxide than with anatase-type titanium
oxide and a change in color difference can be controlled. The
rutile-type titanium oxide is preferably treated with a fatty acid
such as stearic acid or a derivative thereof before use to improve
dispersibility because the glossiness of the film can be further
improved.
[0022] When the rutile-type titanium oxide is used, it is
preferably subjected to adjustment of particle size and removal of
coarse particles by use of a purification process before added to
the polyester. As for industrial means for conducting the
purification process, for example, a jet mill or a ball mill can be
used as crushing means, and dry or wet centrifugal separation can
be used as classification means. These means may be used in
combination of two or more to purify the titanium oxide
stepwise.
[0023] Inert particles of one type may be used alone or inert
particles of two or more types may be used in combination.
[0024] To have the inert particles contained in the polyester, it
is preferred to use any of the following methods, i.e. (a) a method
of adding the inert particles before the completion of a
transesterification reaction or esterification reaction or before
the start of a polycondensation reaction during synthesis of the
polyester, (b) a method comprising adding the inert particles to
the polyester and melt-kneading them, (c) a method comprising
producing master pellets by adding a large amount of the inert
particles by the above method (a) or (b) and mixing the master
pellets with a polyester containing no additive to have a
predetermined amount of the additive contained in the polyester,
and (d) a method of using the master pellets produced in the above
(c) as they are.
[0025] When titanium oxide is added by use of the above method (a)
of adding it during synthesis of the polyester, it is preferably
added to the reaction system as slurry having the titanium oxide
dispersed in glycol.
[0026] It is particularly preferred to use the above method (c) or
(d).
[0027] In the present invention, it is preferred to filter a molten
polymer by use of a nonwoven fabric filter made of stainless steel
wires having a wire diameter of not larger than 15 .mu.m and having
an average opening size of 10 to 100 .mu.m, preferably 20 to 50
.mu.m, as a filter before film formation, i.e. before the molten
polymer is discharged from the slit to form a film. By carrying out
this filtration, agglomeration of particles which are generally
liable to form coarse agglomerated particles is inhibited, and a
film having few coarse foreign matters can be obtained.
Additives
[0028] The polyesters constituting the layers A and B may contain,
as additives, aluminum oxide, magnesium oxide, organic fillers such
as an acrylic resin, an urea resin and a melamine resin, other
resins such as polyethylene, polypropylene, an ethylene-propylene
terpolymer and an olefinic ionomer, an antioxidant, an ultraviolet
absorber and a fluorescent brightener as required in amounts that
do not deviate from the scope of the present invention.
[0029] The fluorescent brightener is preferably added in an amount
of 0.005 to 0.2 wt %, more preferably 0.01 to 0.1 wt %, based on
the polyester composition. When the amount of the florescent
brightener is smaller than 0.01 wt %, reflectivity at wavelengths
of around 350 nm is not satisfactory, and a reflecting plate with
unsatisfactory illuminance is obtained disadvantageously.
Meanwhile, when the amount is larger than 0.2 wt %, the color of
the fluorescent brightener appears disadvantageously. As the
florescent brightener, OB-1 (product of Eastman Co.), Uvitex-MD
(product of Ciba-Geigy Co., Ltd.) or JP-Conc (product of Nippon
Chemical Industrial Co., Ltd.) can be used, for example. Further, a
coating agent containing an antioxidant, an ultraviolet absorber, a
fluorescent brightener and the like may be applied to at least one
surface of the present film as required.
Film Production
[0030] The laminated film of the present invention comprises at
least the layer A and the layer B and may also comprise other
layers. The layers A and B exist in contact with each other. The
laminated film of the present invention may take, for instance, a
two-layer structure of layer A/layer B, a three-layer structure of
layer A/layer B/layer A or a four-layer structure of layer A/layer
B/layer A/layer B. Alternatively, the laminated film may take a
structure comprising 5 or more layers including the above
structures.
[0031] In view of ease and effects in film production, the
two-layer structure or the three-layer structure of layer A/layer
B/layer A is particularly preferred. Further, other layers may be
laminated on one or both surfaces of the film to impart other
functions. As the other layers, a transparent polyester resin
layer, a thin metal film, a hard-coating layer and an ink absorbing
layer can be used, for example.
[0032] The thickness of the layer A is preferably 6 to 60 .mu.m,
more preferably 5 to 50 .mu.m. Meanwhile, the thickness of the
layer B is preferably 30 to 230 .mu.m, more preferably 40 to 220
.mu.m. Further, the ratio of the thickness of the layer A to the
thickness of the layer B is preferably 1/20 to 1/2, more preferably
1/18 to .
[0033] Next, an example of a method for producing the laminated
film of the present invention will be described. Molten polymers
are extruded from dies by a simultaneous multilayer extrusion
method using a feed block to produce an unstretched laminated
sheet. That is, a molten polymer which forms the layer A and a
molten polymer which forms the layer B are laminated in the form
of, for example, layer A/layer B/layer A by use of a feed block and
extruded from dies. At that time, the polymers laminated in the
feed block retain the laminated form.
[0034] The unstretched sheet extruded from the dies are cooled and
solidified by a casting drum to form an unstretched film. This
unstretched film is heated by roll heating, infrared heating or the
like and stretched in the longitudinal direction to obtain the
longitudinally stretched film. This stretching is preferably
carried out by use of the difference in circumferential speed
between two or more rolls. The stretch temperature is equal to or
higher than the glass transition point (Tg) of the polyester,
preferably Tg to (Tg+70).degree. C. Although varying depending on
required properties of application, the stretch ratios in the
longitudinal direction and the direction perpendicular to the
longitudinal direction (hereinafter referred to as "transverse
direction") are preferably 2.5 to 4.0 times, more preferably 2.8 to
3.9 times. When the stretch ratios are smaller than 2.5 times,
nonuniformity in the thickness of the film becomes worse and a good
film cannot be obtained, while when the stretch ratios are larger
than 4.0 times, ruptures are liable to occur during film production
disadvantageously.
[0035] The longitudinally stretched film is then subjected to
transverse stretching, heat-setting and heat relaxation
sequentially to obtain a biaxially oriented film. These treatments
are carried out with the film running. The transverse stretching is
started from a temperature higher than the glass transition point
(Tg) of the polyester and carried out while the temperature is
elevated to a temperature higher than Tg by 5 to 70.degree. C. The
elevation of the temperature in the transverse stretching process
may be continuous or stepwise (sequential) but is generally
sequential. For example, the transverse stretching zone of a tenter
is divided into a plurality of zones along the film running
direction and a heating medium of given temperature is flown in
each zone to elevate the temperature. Although varying depending on
required properties of application, the transverse stretching ratio
is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times.
When the stretch ratio is smaller than 2.5 times, nonuniformity in
the thickness of the film becomes worse and a good film cannot be
obtained, while when the stretch ratio is larger than 4.5 times,
ruptures are liable to occur during film production.
[0036] When the melting point of the polyester is Tm(.degree. C.),
the transversely stretched film is preferably heat-treated at
(Tm-20 to 100).degree. C. at a constant width or a reduction in
width of not higher than 10% with both ends of the film held to
reduce heat shrinkage. When the heat treatment temperature is
higher than the above range, the flatness of the film deteriorates
and nonuniformity in thickness becomes great disadvantageously.
Meanwhile, when the heat treatment temperature is lower than
(Tm-80).degree. C., heat shrinkage may increase. Further, to adjust
heat shrinkage in a range of lower than (Tm-20 to 100).degree. C.,
it is possible to cut off the held ends of the film and adjust the
take-over speed in the longitudinal direction of the film so as to
relax the film in the longitudinal direction while the heat-set
film is allowed to cool to room temperature. Speed of rolls at the
exporting side of the tenter is controlled as means of relaxation.
As for the relaxation ratio, the speed of rolls is slowed down with
respect to the film line speed of the tenter, and a slowdown or
relaxation (hereinafter referred to as "relaxation ratio") of
preferably 0.1 to 1.5% is conducted. A relaxation ratio of more
preferably 0.2 to 1.2%, much more preferably 0.3 to 1.06, is
conducted to adjust heat shrinkage in the longitudinal direction.
As for the transverse direction of the film, desired heat shrinkage
can be obtained by decreasing the width by the time when both ends
are cut off.
[0037] The thus obtained laminated film of the present invention
may have a heat shrinkage at 85.degree. C. in the two directions
perpendicular to each other of 0.7% or lower, more preferably 0.6%
or lower, most preferably 0.5% or lower. The thickness of the
biaxially stretched film is preferably 25 to 250 .mu.m, more
preferably 30 to 220 .mu.m, much more preferably 40 to 200 .mu.m.
When the thickness is 25 .mu.m or smaller, reflectivity lowers,
while when it is larger than 250 .mu.m, an improvement in
reflectivity cannot be expected disadvantageously.
[0038] The laminated film of the present invention can be suitably
used for a reflecting plate, e.g. a reflecting plate for a liquid
crystal display.
[0039] As described above, according to the present invention, a
white laminated film can be provided that has a practically
satisfactory capability of reflecting visible light, can be
produced stably even if inert particles are added in high
concentration and hardly has streak-like defects on the surfaces of
the film. This laminated film can be suitably used as a substrate
for a reflecting plate for a liquid crystal display or an
internally illuminating electrical billboard.
EXAMPLES
[0040] Hereinafter, the present invention will be further described
by use of Examples. Property values were measured in the following
manner.
(1) Film Thickness
[0041] The thickness of film sample was measured at 10 points by
means of an electric micrometer (K-402B of Anritsu Corporation),
and the average was taken as the thickness of the film.
(2) Thickness of Each Layer
[0042] A sample was cut out in a triangular shape, fixed to an
embedding capsule and then embedded in an epoxy resin. Then, a
cross section parallel to the longitudinal direction of the
embedded sample and having a thickness of 50 nm was cut out of the
embedded sample by means of a microtome (ULTRACUT-S) and observed
and photographed at an accelerating voltage of 100 kv by use of a
transmission electron microscope. The thickness of each layer was
measured from the photograph, and the average thickness was
determined.
(3) Reflectivity
[0043] An integrating sphere was attached to a spectrophotometer
(UV-3101PC of Shimadzu Corporation), and reflectivity when a
BaSO.sub.4 white plate was 100% was measured over 400 to 700 nm.
Reflectivity was read from the obtained chart at an interval of 2
nm. The average was determined within the above range and rated
based on the following criteria.
.largecircle.: Reflectivity is 90% or higher in all measured range.
.DELTA.: The average reflectivity is 90% or higher in the measured
range, and reflectivity is lower than 90% at some wavelengths. X:
The average reflectivity is lower than 90% in all measured
range.
(4) Stretchability
[0044] A film was stretched at a longitudinal stretch ratio of 2.9
to 3.4 times and a transverse stretch ratio of 3.5 to 3.7 times to
be formed and it was observed whether the film could be produced
stably. The result was evaluated based on the following
criteria.
.largecircle.: A film can be produced stably for 1 hour or longer.
X: Ruptures occur within 1 hour, and stable film production is not
possible.
(5) Heat Shrinkage
[0045] A film was kept in an oven set at 85.degree. C. in an atonic
state for 30 minutes, the distance between gage marks was measured
before and after a heat treatment, and heat shrinkage (heat
shrinkage at 85.degree. C.) was calculated from the following
formula.
Heat Shrinkage (%)=((L0-L)/L0).times.100
[0046] L0: Distance between gage marks before heat treatment
[0047] L: Distance between gage marks after heat treatment
(6) Glass Transition Point (Tg) and Melting Point (Tm)
[0048] These were measured at a temperature increasing rate of 20
m/min by use of a differential scanning calorimeter (TA Instruments
2100 DSC).
(7) Observation of Film Defects
[0049] A biaxially stretched film having a size of 20 cm.times.20
cm was visually observed under a halogen lamp at a distance of
about 30 cm and an angle of 45.degree. from the film surface.
X: Black streaks are observed. .largecircle.: Black streaks are not
observed.
(8) Assay of Metal Element
[0050] A film was melt-molded at 240.degree. C. to prepare a plate
having a diameter of 5 cm and a thickness of 3 mm, and the plate
was measured by a fluorescent X-ray (SEA1000 of SII). "Containing
substantially no antimony (Sb) element" indicates lower than the
detection limit (e.g. 0 ppm) in the present measurement.
Examples 1 to 4
[0051] 132 parts by weight of dimethyl terephthalate, 18 parts by
weight of dimethyl isophthalate (12 mol % based on the acid
component of polyester), 96 parts by weight of ethylene glycol, 3.0
parts by weight of diethylene glycol, 0.05 parts by weight of
manganese acetate and 0.012 parts by weight of lithium acetate were
charged into a flask equipped with a rectifying column and a
distillation condenser, heated to 150 to 235.degree. C. under
agitation to distill methanol out so as to carry out a
transesterification reaction. After methanol was distilled out,
0.03 parts by weight of trimethyl phosphate and 0.04 parts by
weight of germanium dioxide were added, and the reactants were
transferred to a reactor. Then, while the contents of the reactor
were agitated, the pressure inside the reactor was gradually
reduced to 0.5 mmHg and the temperature inside the reactor was
increased to 290.degree. C. to carry out a polycondensation
reaction. The obtained copolyester showed an intrinsic viscosity of
0.70 dl/g, a melting point of 224.degree. C., a diethylene glycol
content of 2.5 wt %, a germanium element content of 50 ppm and a
lithium element content of 5 ppm. To this polyester resin, inert
particles shown in Table 1 were added. Then, the resin was fed to
two extruders heated to 280.degree. C., and the layer A polymer and
the layer B polymer were combined by use of a three-layer feed
block so that a structure of layer A/layer B/layer A was obtained,
and the polymers were molded into a sheet from a die while the
laminated form was retained. Then, this sheet was cooled and
solidified by a cooling drum having a surface temperature of
25.degree. C. to obtain an unstretched film, and the unstretched
film was then heated at a shown temperature, stretched in a
longitudinal direction and cooled by rolls of 25.degree. C. Then,
the longitudinally stretched film was led to a tenter with both
ends thereof held by clips and stretched in the direction
(transverse direction) perpendicular to the longitudinal direction
in an atmosphere heated to 120.degree. C. Thereafter, the stretched
film was heat-set in the tenter at a temperature shown in Table 2,
subjected to relaxation in the longitudinal direction and side
adjustment in the transverse direction at temperatures shown in
Table 2, and then cooled to room temperature to obtain a biaxially
stretched film. The physical properties of the obtained films as a
substrate for a reflecting plate are as shown in Table 2.
Examples 5 to 13
[0052] A copolyester was obtained in the same manner as in Examples
1 to 4 except that 0.05 parts by weight of manganese acetate was
changed to 0.02 parts by weight of titanium acetate. The obtained
copolyester showed an intrinsic viscosity of 0.68 dl/g, a melting
point of 225.degree. C., a diethylene glycol content of 2.5 wt %, a
titanium element content of 15 ppm and a lithium element content of
5 ppm. To this polyester resin, inert particles shown in Table 1
were added, and films were prepared as shown in Table 2.
Comparative Example 1
[0053] After 85 parts by weight of dimethyl terephthalate and 60
parts by weight of ethylene glycol were subjected to a
transesterification reaction in the usual manner by use of 0.09
parts by weight of calcium acetate as a catalyst, an ethylene
glycol solution containing 10 wt % of trimethyl phosphate was added
as a phosphorus compound in an amount of 0.18 wt % based on a
polymer, and 0.03 parts by weight of antimony trioxide was then
added as a polymerization catalyst. Then, a polycondensation
reaction was carried out at high temperature and under reduced
pressure in the usual manner to obtain a polyethylene terephthalate
having a limiting viscosity of 0.60. This copolyester had an
intrinsic viscosity of 0.65 dl/g, a melting point of 257.degree.
C., a diethylene glycol content of 1.2 wt %, an antimony element
content of 30 ppm and a calcium element content of 10 ppm. To this
resin, inert particles shown in Table 1 were added to form layers A
and B. A film was prepared under conditions shown in Table 2.
Comparative Example 2
[0054] A film was prepared in the same manner as in Comparative
Example 1 except that conditions shown in Tables 1 and 2 were
used.
Comparative Examples 3 and 4
[0055] Films were prepared in the same manner as in Comparative
Example 1 except that conditions shown in Tables 1 and 2 were used.
Since stretchability was extremely low and ruptures often occurred
during film production, film samples could not be prepared.
Comparative Examples 5 and 6
[0056] A copolyester resin was obtained in the same manner as in
Examples 1 to 4 except that 0.04 parts by weight of germanium
dioxide was changed to 0.04 parts by weight of antimony trioxide.
The copolyester resin had an antimony element content of 40 ppm. By
use of this resin, films were prepared as shown in Tables 1 and
2.
Comparative Example 7
[0057] By use of the resin of Comparative Example 1, 14 wt % of
calcium carbonate as inorganic fine particles was added as surface
layers (front face and rear face) of a three-layer film, and 10 wt
% of polymethylpentene resin that was an incompatible resin and 1
wt % of polyethylene glycol were mixed into polyethylene
terephthalate as the resin of the core layer to prepare a film. As
shown in Tables 1 and 2, streaks were noticeable and reflectivity
was poor.
TABLE-US-00001 TABLE 1 Polyester Resin of Layer A Amount of Inert
Particles/Average Type of Copolymerizable % of Particle Diameter
Resin Component Copolymerization Inert Particles (wt %/.mu.m) Tg Tm
Sb Element Ex. 1 PET IPA 12 Barium Sulfate 5.0/1.2 74 225 0 Ex. 2
PET IPA 12 Barium Sulfate 10.0/1.2 74 225 0 Ex. 3 PET IPA 12
Titanium Dioxide 5.0/1.0 75 225 0 Ex. 4 PET IPA 12 Titanium Dioxide
4.0/0.3 74 224 0 Ex. 5 PET IPA 12 Barium Sulfate 3.0/0.7 74 225 0
Ex. 6 PET IPA 12 Barium Sulfate 20.0/1.2 74 223 0 Ex. 7 PET IPA 12
Barium Sulfate 4.0/1.2 74 225 0 Ex. 8 PET IPA 12 Calcium Carbonate
7.5/1.5 75 224 0 Ex. 9 PET IPA 7 Silicon Dioxide 5.0/1.2 76 239 0
(Complete Spheres) Ex. 10 PET NDC 12 Barium Sulfate 25/0.6 81 223 0
Ex. 11 PET IPA 15 Silicone 5.0/1.2 71 220 0 (Spherical) Ex. 12 PET
CHDM 3 Calcium Carbonate 15/2.5 78 243 0 Ex. 13 PET NDC 6 Calcium
Carbonate 2/1.0 79 240 0 C. Ex. 1 PET -- -- Barium Sulfate 5.0/1.5
80 257 30 C. Ex. 2 PET -- -- Titanium Dioxide 3.0/0.3 79 257 30 C.
Ex. 3 PET -- -- Titanium Dioxide 7.5/1.5 80 257 30 C. Ex. 4 PET --
-- Titanium Dioxide 7.5/1.5 79 256 30 C. Ex. 5 PET IPA 12 Barium
Sulfate 15.0/1.2 75 224 40 C. Ex. 6 PET IPA 12 Barium Sulfate
3.0/1.2 74 225 40 C. Ex. 7 PET -- -- Calcium Carbonate 14/1.5 78
255 30 Total Polyester Resin of Layer B Content Amount/Average
Layer Of Type Particle Structure Inert of Copolymerizable % of
Diameter Thickness Particles Resin Component Copolymerization Inert
Particles (wt %/.mu.m) Tg Tm Ratio (wt %) Ex. 1 PET IPA 12 Barium
Sulfate 50/1.2 74 225 A/B/A = 15/70/15 36.5 Ex. 2 PET IPA 12 Barium
Sulfate 45/1.2 74 225 A/B/A = 10/80/10 38.0 Ex. 3 PET IPA 12
Titanium Dioxide 50/1.0 75 225 A/B/A = 20/60/20 32.0 Ex. 4 PET IPA
12 Titanium Dioxide 55/0.3 74 224 A/B/A = 12/76/12 42.8 Ex. 5 PET
IPA 12 Barium Sulfate 50/0.7 74 225 A/B/A = 12/76/12 38.7 Ex. 6 PET
IPA 12 Barium Sulfate 55/1.2 74 223 A/B/A = 15/70/15 44.5 Ex. 7 PET
IPA 12 Barium Sulfate 51/1.2 74 225 A/B/A = 15/70/15 36.9 Ex. 8 PET
IPA 12 Titanium Dioxide 35/1.5 75 224 A/B/A = 15/70/15 26.8 Ex. 9
PET IPA 7 Silicon Dioxide 55/1.5 76 239 A/B/A = 7/86/7 48.0
(Complete Spheres) Ex. 10 PET NDC 12 Barium Sulfate 40/1.2 81 223
A/B/A = 8/84/8 37.6 Ex. 11 PET IPA 15 Titanium Dioxide 35/0.5 71
220 A/B/A = 10/80/10 29.0 Ex. 12 PET CHDM 3 Calcium 35/2.5 78 243
A/B/A = 12/76/12 30.2 Carbonate Ex. 13 PET NDC 6 Calcium 30/1.2 79
240 A/B/A = 6/88/6 26.6 Carbonate C. Ex. 1 PET -- -- Barium Sulfate
20/1.5 80 257 A/B/A = 15/70/15 15.5 C. Ex. 2 PET -- -- Titanium
Dioxide 20/0.3 79 257 A/B/A = 15/70/15 14.9 C. Ex. 3 PET -- --
Titanium Dioxide 30/1.5 80 256 A/B/A = 15/70/15 23.3 C. Ex. 4 PET
-- -- Titanium Dioxide 50/1.5 79 257 A/B/A = 15/70/15 37.3 C. Ex. 5
PET IPA 12 Barium Sulfate 51/1.2 75 224 A/B/A = 15/70/15 40.2 C.
Ex. 6 PET IPA 12 Barium Sulfate 45/1.2 74 225 A/B/A = 12/76/12 34.9
C. Ex. 7 PET -- -- -- (PMX Resin 77 253 A/B/A = 6/88/6 1.7 Added)
Ex.: Example, C. Ex.: Comparative Example PET: Polyethylene
Terephthalate, IPA: Isophthalic Acid, NDC:
2,6-naphthalenedicarboxylic acid In the above table, the amount of
inert particles is the proportion (wt %) of the inert particles to
the total weight of polyester and the inert particles. CHDM:
Cyclohexane Dimethanol, PMX: Polymethylpentene
TABLE-US-00002 TABLE 2 Relaxation Ratio/ Toe-in rate Longitudinal
Transverse Heat Temperature (Relaxationrate Temperature
Longitudinal Stretch Transverse Stretch Setting for Cutting Both in
transverse of the Stretch Temperature Stretch Temperature
Temperature Ends direction) Toe-in rate Ratio (.degree. C.) Ratio
(.degree. C.) (.degree. C.) (.degree. C.) (%) (.degree. C.) Ex. 1
2.9 95 3.7 120 210 0.5/130 2 150 Ex. 2 2.9 95 3.7 120 210 0.5/130 2
150 Ex. 3 3.4 90 3.7 120 210 0.4/120 1 130 Ex. 4 2.9 90 3.5 120 210
0.7/150 3 130 Ex. 5 2.9 95 3.7 120 210 0.5/150 3 150 Ex. 6 2.9 90
3.7 120 210 1.0/150 -- -- Ex. 7 2.9 90 3.7 120 210 0.5/120 3 150
Ex. 8 2.9 95 3.7 120 210 0.5/130 2 150 Ex. 9 3.0 90 3.8 125 200
0.5/115 2 120 Ex. 10 2.8 95 3.7 125 200 0.6/120 2 130 Ex. 11 2.9 85
3.9 115 190 0.7/140 1 140 Ex. 12 3.0 95 3.7 120 205 0.5/130 1 150
Ex. 13 3.4 90 3.5 120 210 0.8/130 2 140 C. Ex. 1 2.9 90 3.7 120 210
-- -- -- C. Ex. 2 2.9 90 3.7 120 210 0.5/130 2 150 C. Ex. 3 3.4 90
3.7 120 210 0.5/130 3 150 C. Ex. 4 3.4 90 3.7 120 210 0.5/130 3 150
C. Ex. 5 2.9 90 3.5 120 210 0.5/130 3 150 C. Ex. 6 2.9 90 3.7 120
210 0.5/130 1 130 C. Ex. 7 3.4 92 3.6 130 230 -- -- -- Biaxially
Stretch Heat Shrinkage(%) Thickness Evaluation of Observation at 85
(.degree. C.) (.mu.m) Reflectivity of Streaks Longitudinal
Transverse Stretchability Ex. 1 150 .largecircle. .largecircle. 0.1
0.1 .largecircle. Ex. 2 150 .largecircle. .largecircle. 0.1 0.1
.largecircle. Ex. 3 100 .largecircle. .largecircle. 0.2 0.2
.largecircle. Ex. 4 100 .largecircle. .largecircle. 0.1 0.1
.largecircle. Ex. 5 170 .largecircle. .largecircle. 0.2 0.1
.largecircle. Ex. 6 75 .largecircle. .largecircle. 0.1 0.6
.largecircle. Ex. 7 50 .largecircle. .largecircle. 0.1 0.1
.largecircle. Ex. 8 150 .largecircle. .largecircle. 0.1 0.1
.largecircle. Ex. 9 188 .largecircle. .largecircle. 0.2 0.1
.largecircle. Ex. 10 200 .largecircle. .largecircle. 0.1 0.1
.largecircle. Ex. 11 188 .largecircle. .largecircle. 0.3 0.2
.largecircle. Ex. 12 225 .largecircle. .largecircle. 0.3 0.1
.largecircle. Ex. 13 200 .largecircle. .largecircle. 0.1 0.1
.largecircle. C. Ex. 1 150 .DELTA. X 0.8 0.8 .largecircle. C. Ex. 2
150 .DELTA. X 0.1 0.1 .largecircle. C. Ex. 3 -- -- -- -- -- X C.
Ex. 4 -- -- -- -- -- X C. Ex. 5 100 .largecircle. X 0.2 0.2
.largecircle. C. Ex. 6 150 .largecircle. X 0.4 0.3 .largecircle. C.
Ex. 7 50 X X 0.3 0.3 .largecircle. Ex.: Example, C. Ex.:
Comparative Example
* * * * *